PROJECT SUMMARY The blood system is a developmental hierarchy maintained by rare hematopoietic stem cells (HSCs) capable of extended self-renewal and multilineage differentiation. Because of their ability to fully reconstitute the blood system upon transplantation, HSCs are a highly valued therapeutic cell type. During my Ph.D. training with Dr. John Dick, I have gained expertise and contributed to understanding of human HSCs from umbilical cord blood (Nat Immunol 2010; Science 2011). In my postdoctoral training with Dr. George Daley, I have directed all my efforts and expertise to the generation of HSCs and other valuable human blood cells, such as transfusable red blood cells, from patient induced-pluripotent stem cells (iPSCs). My work has demonstrated the feasibility of this important goal by showing that human iPSC-derived blood precursors can be converted (or respecified) into transplantable multilineage progenitors using transcription factors: HOXA9, ERG, and RORA (Cell Stem Cell 2013). The idea of respecifying progenitors into stem cells is a promising approach, however we are still short of generating true HSCs. In the mentored part of my research proposal, I will focus on identifying combinations of transcription factors that respecify iPSCs into HSCs with long-term multilineage transplantation potential. In the independent phase, I will study the role of these regulatory networks in normal hematopoiesis. Respecified iPSC progenitors are a particularly potent source of red blood cells in vitro and in vivo. Human erythrocytes undergo globin switching in vivo to express adult hemoglobin mimicking the fetal-to-adult globin switch that occurs after birth. For this reason, I have initiated the study of two congenital anemias using iPSC lines from patients with Diamond Blackfan anemia and sickle cell anemia. By using the transcription factors to engraft iPSC-derived progenitors in mice, I will create the first in vivo models of human blood disorders, with the goal of interrogating the underlying disease mechanisms and as a platform for drug testing (Aim 2a). In the independent phase, I will delve deeper, using the iPSC factor system to study myelodysplastic syndromes with a chromosome 5q deletion to dissect the contribution of individual genes within the deletion interval to disease pathobiology (Aim 2b), which will identify potential avenues for targeted therapies. Dr. Daley is an internationally respected investigator in stem cell biology, the Samuel E. Lux IV Professor of Hematology, and serves as the Director of the Stem Cell Transplantation Program at Boston Children's Hospital (BCH). Dr. Daley has mentored 36 principal investigators and group leaders in industry, and has received the A. Clifford Barger Excellence in Mentoring Award from Harvard Medical School. BCH is a prestigious research institute and a pediatric medical center. BCH is part of a network of medical and academic institutions within the greater Harvard research and medical community, that includes Harvard Medical School, Dana-Farber Cancer Institute, Brigham and Women's Hospital, Beth Israel Deaconess Medical Center, Harvard Stem Cell Institute, and others. This rich environment provides a superb opportunity for a young scientists to train, carry out high impact research, and foster professional interactions. Dr. Daley and I have developed a detailed career development plan that will allow me to acquire the needed technical, mentorship, and leadership skills. I will be further guided by a committee of senior leaders in stem cell biology: Drs. Leonard Zon, Stuart Orkin, and Gordon Keller. The support of this K99/R00 award will allow me to dedicate my full energies to carry out this ambitious project with the goal of producing several high-impact papers by the end of mentored phase. Using my expertise in hematopoiesis, pluripotent stem cells, and primary human systems, I will apply for R00 funds to establish an independent research program at a top institute with a reputation as a leader in stem cell biology. I believe that this combination of skills and an innovative research plan outlined in this proposal will allow me to establish myself as an independent investigator. My career goal is to become a leader in the field of stem cell biology, to carry out a diverse and collaborative research program that provides fundamental insights into basic biology, while creating real opportunities for translation, drug design, and cell-based therapies.